In this document, the term “electrical network” will normally be used to refer to any general electrical system whereto a photovoltaic system is connected. Currently, photovoltaic systems connected to the network are becoming a standard electrical energy generation technology in developed countries. They began, a few years ago, as de-centralised, isolated direct current installations, and, today, photovoltaic modules combined with inverters represent one of the mature electrical generation technologies in a future environment of large-scale renewable generation.
Said photovoltaic systems are composed of a set of solar panels that supply an inverter equipment (DC/AC converter), with or without a transformer, which is connected to the electrical network through a meter that makes it possible to determine the energy supplied by the installation. In some cases, the inverter equipment may include a DC/DC converter.
The inverter equipment usually operates at a variable power, seeking at all times the maximum output power point. Said power is dependent on the energy that reaches the inverter from the solar panels and, therefore, from the irradiance conditions, and the temperature. On the other hand, the inverter is automatically disconnected when the energy supplied thereto is below a given value, that is, when the irradiance is weak, below a given threshold.
In the event that the inverter includes a DC/DC converter, the latter will adapt the voltage provided by the panels to a constant value that will supply the DC/AC converter, which will always automatically operate with the same input voltage. Sometimes an accumulator or battery bank is used in the photovoltaic system in order to store the energy produced during the day, which is used at night and during cloudy periods. A load regulator controls the system operativity and the current flow to and from the battery in order to protect it against overcharge, overdischarge, etc.
Currently, there are two development fronts in regards to photovoltaic solar energy: in the first place, maximising energy production and, in the second place, allowing for the network integration of photovoltaic plants. Due to the growth of renewable energies, it is necessary for photovoltaic plants to be able to provide services to the network and contribute to the stability thereof; for this reason, it is increasingly necessary, and the more so in large photovoltaic plants, to solve the problem of their integration into the electrical network.